I have a 2008 Suburban LTZ with 30k miles. It has the factory HD towing package which includes 3.73 gears, air suspension (love this), and a tranny cooler.

The truck tows fine to the local ramp, over moderate hills, etc. But on the longer tow trips over big, long grades it struggles. Last year on the way to Shasta I saw the tranny fluid go up to 235 degrees.

We are headed back to Shasta in a few weeks and I'm not axious to see this happen again. Back then I was towing in 'D' and I've since switch to towing in '3' which seems to have helped.

In addition to flushing my tranny fluid, now I'm wondering if it would be beneficial to swamp out the OEM tranny cooler for something a little beefier.

Yes with the biggest cooler you can find . The deep pan will also help. When you have your fluid flushed have synthetic fluid put in it will lower trans temp about 20 degrees. You dont want the trans much over 200 at 235 you will cause damage.

I would replace it for sure. I had the HD tow package on my Avalanche and the tranny lasted 60k miles before it let go and then I put in a bigger cooler, new converter and upgraded the clutches. I think the bigger cooler and pan will save you about $2,500 in the long run.

Depends on wht type of cooler it has. If it's a cheapy tube and fin type then ditch it and get a good stacked plate cooler. If it's already stacked plate then leave it. Also if you get a deeper pan see if you can get a trans filter for a deep pan that has an extension on the pickup so it gets fluid from the bottom of the pan, or if you can make one. Deeper pan and synthetic fluid are both good ideas though.